The fashion world doesn't celebrate New Year with you civilians, you know. We do our all-change moment in September, when we have a nice tan and the light is flattering. The first few weeks of January are vile: you are flat broke and spotty from too many Quality Street and suffering Baileys withdrawal symptoms. Anything that involves a mirror is to be avoided at all costs, and that includes sales shopping. In an ideal world, one would avoid this chunk of the year by being in Thailand disguising a slight Tiger-beer belly with the use of strategic yoga positions but should that prove impractical, the next best thing is to put your feet up, ignore the resolution bores and wait for 2011 to really begin, fashionably late, in a few weeks' time.

Fashion has a ready-made crystal ball, in that this spring/summer's designer collections were shown on the catwalks last September. But the designer trends take on a life of their own once real people get their hands on them. The overarching aesthetic of 2010 was an ultra-youthful, sharp, staccato look, epitomised by stick-thin legs poking out of ankle boots and short, stiffly carved dresses. At the pretty, commercial, weekly mag-friendly end of the spectrum, this meant the Whitney Port/Olivia Palermo red-carpet look: all bare legs, fierce ankle boots and sweet smiles. At the other end of the scale – but channelling the same mood – were Lady Gaga and the Italian fashion-editor-extraordinaire Anna Della Russo, who added fruit hairpieces and feather epaulettes to the silhouette.

This year looks set to see a changing of the guard. A softer-edged look is coming into focus. Yesterday, many fashion blogs were running a first-look picture from the new Valentino advertising campaign, shot by David Sims in the Valentino Paris mansion on the Place Vendôme. The model is lounging on a sofa, one foot tucked under the other, giving a subtly different message to the dominant pose of the past year, in which the model stands stiff as a toy soldier, albeit one dressed in Barbie's frock.

The toy soldier brigade won't back down straight away, of course – and why would they, since if you've got the legs for it, there's no denying toy-soldier-Barbie is a hot look. The first adjustment will come when the movie Black Swan, which stars Natalie Portman as a ballet dancer, opens later this month. The ballet trend has been gathering pace – Karl Lagerfeld at Chanel and Sarah Burton at Alexander McQueen put tutu shapes and fabrics on the Paris fashion week catwalk recently – and the film's costumes, designed by cult New York label Rodarte, are likely to fuel ballet fever. A post-Strictly nation is ready for a new dance craze. At Frame in Shoreditch – probably London's hippest fitness studio – ballet is the new Pilates.

The tutu trend. Photograph: Mauricio-Jose Schwarz / Alamy/Alamy

Hot on the heels of the corps de ballet will come the next wave of the new-look invasion, when the season's clothes hit shopfloors. For two years, dissenting voices within the fashion industry have been berating designers for the impractical brevity of their hemlines, and 2011 looks set to be the season when BTK – Below the Knee – finally happens. From the crisp, minimalist floor-length skirts at Jil Sander to the 70s-peacock silk flared-leg jumpsuits at Marc Jacobs to Topshop's new-look teen-clubbing gear (crop tops and cropped kick flares, with crimped hair), the silhouette is longer.

But more important even than the change in hemline is the change in attitude. There is more of a swagger to 2011's look. That there was a hunger for this was clear from the hysteria greeting Tom Ford's first own-label womenswear show in September. At his private salon-style show, the women sashayed, laughed and twirled on the catwalk, a stark contrast to the marching parades of late.

Needless to say, it was a lot more fun, and many in the industry will be looking to channel a bit of that energy, that swagger, when the next round of shows begin in February. (Those in search of a bite-size piece of the next-season fashion pie before then need look no further for inspiration than the fruit bowl. Miuccia Prada's banana prints and Stella McCartney's lemon motifs are the easy-win of the spring/summer, and already available on a high street near you.)

But this spring, London fashion week can expect to be thoroughly overshadowed on the fashion calendar. A royal wedding – and one where the bride has Cheryl Cole's hair and a model-perfect figure – is not a day that can be upstaged. No catwalk frock, however beautiful or controversial, can expect to reach anywhere close to the audience numbers that Kate Middleton's wedding dress will be seen by. Come 29 April the wedding dress – and, to a lesser extent, the wardrobe of the entire wedding party – will be examined for formality, expense, colour, reference, and all the meanings contained therein. Frankly, if you want to be sure to be wearing 2011's hottest look this year, look no further than the nearest long white dress.